Apparatus for purposes of bending and/or tempering a glass mass to toughen the glass for use as a safety glass for vehicles are known in the prior art. It is also known from the prior art that the glass mass may be brought to its deformation temperature to achieve this result thermally during movement of the glass mass through a lehr or heating oven.
One representative disclosure of the prior art is U.S. Letters Pat. No. 3,084,526 to R. E. Richardson. The Richardson patent relates to apparatus for bending a sheet of glass for use in the manufacture of automobile windshields and rear windows. The apparatus is disclosed as a multipart skeleton mold which supports the sheet of glass which may be provided with a compound bend during transit with the mold as the mold moves through the heating oven.
According to Richardson, if a complex bent shape is to be achieved, those areas of the glass sheet which will be formed to a compound shape, for example, provided with a sharply curved contour, will be subjected to heat of greater intensity than the intensity of heat at other areas of the glass sheet carried on the mold. A localized heating of the glass sheet may be the result of a number of heating devices carried by the mold, itself.
Richardson, however, recognizes that the glass sheet which is subject to localized heating may be heated too rapidly, and, as a consequence, the glass sheet may sink in various places within its surface area. To overcome this problem, Richardson describes the use of one or more nozzles along the heating oven to blow cold air on the glass sheet at times which are determined for the purpose of cooling the glass sheet within areas as determined by the localized heating. The cooling air, thus, will prevent sinking of the glass.
The prior art also discloses that a glass mass, such as a sheet of glass may be moved through a heating oven while supported on a conveyor system comprised of cylindrical rollers or bent transportation rollers, if it is desired to manufacture a glass sheet bent to some shape. Transportation rollers which are bent in a desired shape have been described in French Pat. Nos 1,476,785 and 2,372,463. Briefly, these transportation rollers are surrounded by flexible tubular sheaths, which are rigid in rotation and rotate on the bent support.
The glass masses which move along these conveyor systems oftentimes deform within the hot section of the heating oven The deformation characterized by a small, unwanted bending normally results from a non-uniform support of the glass mass throughout its entire surface area.
The use of one or more nozzles, according to the Richardson teaching, along the heating oven to blow cold air on the glass mass to prevent sinking or deformation within localized areas has not been considered possible or, if possible, practicable under circumstances that the glass mass is moved by a conveyor system including either cylindrical or bent rollers. The Richardson operation is carried out on a glass mass which is stationary on the conveyor system.
According to the prior art, small, unwanted deformation in the glass mass may be remedied by directing a flow of gas at high temperature toward the glass mass from a location below the glass mass. The flow of gas will impinge upon the glass mass within regions between the rollers of the conveyor system. Typical of prior art of this type are Canadian Pat. No. 859,647 and German Offenlegungsschrift 2,741,098. Both of these references discuss that the purpose of the flow of gas, at some pressure, is to balance a part of the weight of the glass mass supported by the conveyor system. According to the references, the pressure which is exerted by the flow of gas is exerted at a constant value throughout the conveyor system, laterally of the width of the glass mass and its direction of movement. Thus, the flow of gas is indicated to support the glass mass uniformly across its width, and the additional or non-supported weight of the glass mass acting on the rollers is sufficient to generate a rubbing force necessary for transport of the glass mass by the conveyor system through the heating oven.